Human Nature in Departures and the Dunes

Several themes have emerged from reading and responding to The Woman in the Dunes: some of you have noted that Niki's plight resembles an existential struggle; others have discussed the theme of  freedom versus responsibility through Niki's first rejecting, and then ultimately accepting his predicament; several have also remarked that the novel evokes a strong idea about the meaning of work. 

Here's the prompt: What theme (or themes) are evident in Yojiro Takita's film, Departures. Compare the plights of Daigo Kobayashi and Niki Jumpei. How are they similar? How are they different? What does this suggest about human nature?